History does not record much widespread use of these implements prior to the middle or late nineteenth century. The bronze cestra that were used by ancient encaustic painters are close relatives. Although there is a definite distinction between the painting knife and the ordinary palette knife, the technique is always referred to as palette-knife painting.
Palette Knives
For mixing colours on the palette or slab and for general studio purposes. Slender, limber blades, four to six inches long, with tapered and rounded tips, both with straight and angular tangs. Angular ones are designed to keep knuckles out of the paint.
Painting Knives
Thin, delicate, very sensitive blades, sometimes welded to long handles, used for direct painting—the application and manipulation of paint on canvas. Obtainable in a multitude of shapes, styles, and sizes, you should, always take care of them and not abuse them because they are fragile.
Spatulas or Paint Knives
Very finely tempered large, strong, flexible counterparts of palette knives, with straight forms, bluntly rounded ends, and sturdy construction, used for mixing and grinding, stirring, and other heavy-duty operations. The 6-inch blade is a typical size. Best ones come from cutlery, hardware, or paint-factory supply sources. The right kind for paint use is tempered to bend at the proper point, not too near the handle.
Putty Knife (Palette Knife)
A putty knife will be useful for scraping dry paint from the palette. One should refrain from employing a painting knife for this purpose because even the slightest injury to the blade will make it useless as a painting instrument.
Scraper
Another useful instrument is a scraper. It is convenient for scraping off a dried impasto and likewise for scraping into a wet paint when one wishes to reveal the underpainting. You can use sandpaper to scrape an old paint layer. One should choose a finer or coarser grade of the abrasive, depending on the thickness of the paint layer.
Three Great Tools
These tools are of great importance; often a major part of a painting will require their use. Three knives, each one with different properties,
are necessary.
The first knife is designed for underpainting. It is made with a firmer blade than the other two knives so that the stiff, undiluted paint used for underpainting can be applied vigorously enough to fill the interstices of the canvas.
The middle knife is a delicate instrument with a tapering, elastic blade that responds readily to the dictates of the artist’s fingers. It is suitable for both detail work and for applying paint in broad areas.
The last knife is usually called a blender. Large surfaces of paint can be blended and smoothed with this knife; it is useful not only for such work as finishing the underpainting of large surfaces but also in finishing
the painting itself.
Trowel-shaped knife
The trowel-shaped knife is not very suitable for painting. For painting small areas, the blade of a knife should be 3 inches long, but for painting larger surfaces, a 4-inch blade is more convenient. The proper degree of elasticity of a blade is also very important. A stiff blade will do well in underpainting, but for the final execution of a painting, we shall need an elastic one.
When To Use a Painting Knife
Ground Support
First, we must know when the employment of a knife is indicated. It is indicated whenever the canvas is used as a support. Painting knives are not suitable for work on panels. Panels are rigid and this makes the use of a knife awkward because there is no rapport between the vibrating blade and the rigid surface. Neither does the knife work well on toothless surfaces, that is, surfaces that are perfectly smooth; here the knife is inclined to slide and slither. This happens because the knife, in manipulating the paint, cannot force some of the paint into the interstices of the fabric.
In addition to the character of the support and the viscosity of the paint the nature of the knife blade must be considered. It cannot be overemphasized that the blade must have just the right degree of elasticity. A stiff blade requires extra pressure which makes the mass of paint squeeze out from under it. An over-elastic blade, on the other hand, does not have the power to move the paint efficiently. Short narrow blades, useful for certain manipulations, are not as well adapted for blending and smoothing out large surfaces as the wider and longer blades.
To become familiar with the working of the knives, students should practice on pieces of waste canvas placed on soft support such as a pile of newspaper. Stretchers are unnecessary. The smooth surface of cardboard, such as we employed for exercises with the brushes, will not provide the proper conditions for exercises with painting knives.
How To Use Painting Knives
The three knives shown should be used in succession, alternately
applying more and less pressure on the canvas. Soon it will be clear that when the knife is held at a certain angle, it leaves considerable paint on the surface, and that a different angle is better for spreading the paint thinly.
However, it is not only a particular angle of the knife that is responsible for the effect achieved, but also, in a large measure, it is the amount of pressure applied. Pushing a thin layer of paint into the interstices of grainy fabric requires greater pressure than moving paint on fabric with comparatively little grain.
When scraping a thin layer of surplus paint from the surface of a canvas, hold the edge of the knife at a narrow-angle, fairly close to the canvas. Exert appreciable pressure and always move the knife away from yourself, rather than toward yourself. For blending large surfaces, and to produce smooth surfaces, the blade of the knife should rest flat or almost flat on the canvas. Knife Number 2 should be used for this purpose. When blending colors, it is imperative to wipe the blade after every stroke and clean off all clinging paint.
To produce strong color effects by means of a knife, two or more colors should be taken up on the blade and, with little or no previous mixing, applied to the canvas in a few strokes. The longer the colors are worked with the knife the more thoroughly they become intermixed—and hence the duller they will look.
While practising these exercises, the beginner may observe that he is able to produce extraordinary colouristic and textural effects similar to effects seen in the works of skilful painters. This could suggest that such effects may result from the particular nature of the instrument and the intrinsic beauty of the colours, rather than from the virtuosity of the artist.
Taking Care of Painting knives
First of all, the blades must always be kept immaculately clean, otherwise, they will mar the painting surface. The blades are not subject to rust, however, even when not in use. They are protected by an infinitesimal coating of protective oil that always remains on the metallic surface after all the paint has been cleaned off the blade.
But painting knives do have a characteristic that needs careful watching—through frequent use, the blades may develop edges sharp enough to endanger not only fingers but the canvas as well. If this happens, the sharp edges should be dulled. To do this, hold the knife upright against a piece of carborundum paper and rotate the edges. During this process, a burr will form on both sides of the blade. This burr should be sanded off with carborundum paper.